A numerical study on the dynamics of droplet impingement

Numerical simulations of a single as well as multiple liquid droplets impinging onto a solid substrate have been performed. The objective of this thesis is to understand the hydrodynamics of the impingement process particularly the interaction between successive droplets. The basic flow solver for modeling free surface flows has been modified to incorporate a dynamic contact angle at the droplet boundary. Formulation based on such a modified boundary condition provides a comprehensive model for better understanding of hydrodynamic aspect of the impingement process. The Navier-Stokes equations are solved using a finite volume formulation. A two-step projection method is used along with a fixed non-uniform staggered rectangular grid. The free surface of the liquid is tracked by the volume-of-fluid method with a second order accurate piecewise-linear scheme. A continuum surface force model is used to calculate the surface tension force.; To gain fundamental understanding of the droplet deformation process, the impingement of a single droplet is examined first. The overall impingement process has been outlined. The effects of several key fluid parameters on the collision behavior are examined. These include: Advancing and receding contact angles, surface tension and viscosity. Study indicates viscosity has a dampening effect on fluid motion; increase in surface tension reduces the maximum spread diameter and increases the recoiling frequency.; The study is further extended to multiple droplet impingement case where the main focus was to examine the effect of droplet parameters such as droplet impact velocity and inter-droplet spacing onto the spread of combined droplet. It has been observed that the inter-droplet spacing determines the spreading mode of the leading droplet when the collision occurs. The spreading and recoiling of droplets as well as the internal flow field are studied.; The numerical results are compared with experimental data and are in general agreement within the confines of the experiment.